#1 Can each burner utilize the full 1800 watts or is each burner maxed at 900 watts?
If each burner would run at 1800 watts, then it would be a 3600W unit, which it is not. Each burner will max out at 900W if both are dialed/selected to full power.
#2 Can a 9 1/2 inch diameter pot (stockpot) be used on the larger (8 inch diameter) cooking element on the 24" cooktop?
It would be just fine. The heat starts in the middle.